Among the medical diagnosis methods using radioactive tracer compounds, many of the radioactive nuclides used in a PET (Positron Emission Tomography) diagnosis have a short half-life and, for example, the half-life of an 18F− ion is about 110 minutes. In order to introduce these radioactive nuclides efficiently into tracer compounds to make the compounds radioactive, a time-saving work will be needed.
Also, since [18O]—H2O water serving as a source material of the 18F− ion is expensive, reuse of the [18O]—H2O water is desired in order to attain cost-down of the PET diagnosis.
Because of the short life of the radioactive nuclides that are put to use, the period of time that can be used for the PET or the like is limited and, for the synthesis of compounds labeled with reduction of time in terms of minutes and a high synthesis rate are simultaneously demanded.
Two methods can be mentioned as a method for producing an organic solvent solution of an 18F− ion by separating the 18F− ion from [18O]—H2O water.
One of the two methods is a method of passing [18O]—H2O water containing the 18F− ion through a column filled with an anion-exchange resin and allowing the 18F− ion to be trapped onto the resin so as to separate the [18O]—H2O water (conventional method 1). With use of an aqueous solution of potassium carbonate, the trapped 18F− ion is reeluted into the aqueous solution to be collected. The collected aqueous solution is subjected to vacuum concentration and, after water is completely removed, the 18F− ion is dissolved in an organic solvent that is used in an organic reaction, so as to obtain an organic solvent solution of the 18F− ion. The concentration of the 18F− ion can be adjusted by the amount of the organic solvent added during this process.
The other one is a method of trapping the 18F− ion onto a glassy carbon rod-shaped electrode and performing solvent exchange from the [18O]—H2O water to an organic solvent (conventional method 2). The [18O]—H2O water from which 18F− has been separated by this method can be expected to be capable of being reused because of not containing eluted organic substances. An apparatus for separating an ion from an [18O]—H2O aqueous solution is reported in Patent Document 1 and Non-patent Documents 1 and 2.
A basis structure of this apparatus is described in detail in Non-patent Document 1. By using a cell having a glassy carbon rod-shaped electrode and a platinum electrode and applying a voltage with the glassy carbon rod-shaped electrode serving as a positive electrode, the 18F− ion is deposited onto the electrode, so as to separate the 18F− ion from the [18O]—H2O water. Then, the 18F− ion deposited onto the positive electrode is collected into an organic solvent (dimethyl sulfoxide (DMSO)) by switching the glassy carbon rod-shaped electrode to a negative electrode, and the collected 18F− ion is supplied to a reaction of the 18F− ion with an organic compound.
Here, Non-patent Document 2 for the first time has reported a technique of depositing an 18F− ion onto a graphite-form carbon electrode with regard to a combination of a graphite-form carbon electrode and a platinum electrode.    Patent Document 1: Japanese Published Patent Publication No. 2005-519270    Non-patent Document 1: Appl. Radiat. Isot. 2006 (64) 989-994.    Non-patent Document 2: Appl. Radiat. Isot. 1989 (40) 1-6.